1. Field of the Invention
The present invention relates to modular communications systems, particularly ISDN communication systems each of which comprises a switching unit having a digital switching matrix and a central control device and comprising an administration data server which serves for the control of the system-oriented periphery and for the storing of system files, as well as comprising further program control modules constructed in a job-oriented manner, a system bus connecting all program control modules, program-control module-associated dependability modules and a dependability security dependability sub-module in the switching unit hierarchy which ranks higher over the program-control module-associated dependability system modules, and further comprising at least one output equipment for the display of errors.
2. Description of the Prior Art
In communication systems, information are through-connected or switched between terminal equipment, these information involving only one type of communication in the simplest case, but increasingly involving a number of types of communication of voice, picture, text or data. ISDN communication systems are particularly suitable for processing all types of communication. ISDN communication systems are already known which enable the simultaneous transmission of different types of communication in uniform digital structure under one telephone number, enabling transmission at a subscriber terminal via a single lead pair. In such an ISDN communication system, as described in ISDN im Buero, special edition of Telcom Report and Siemens Magazin COM, the entire system structure is based on function modules, i.e. the hardware is modularly constructed and the software is modularly structured. The essential modules are a through-connection module which comprises a digital switching matrix array and a central control device, as well as an operation and data module which serves for the control of the system-oriented periphery, as well as for storing system files. The term "receiver" has become common for modules such as the operation and data control module which respectively fulfills specific tasks by means of individual program controls usually realized by multi-processor arrangements. Further known servers, in addition to the operation and data server, are thereby a voice information server which offers the connected subscribers the possibility of re-routing their telephone connection to what are referred to as voice-mail boxes and a text and fax server with which, among other things, the conversion of a message from teletex to telefax is possible in cases in which there is no terminal equipment capable of teletex at the receiver. Further, the picture screen text servers for promoting service procedures for the communication type of picture screen text and special terminal receivers are also known which simultaneously process the request of a plurality of multi-functional terminals. By way of a bus system, the through-connection module is integrated with all other program control modules to form an overall system. The control of all communication activities is sequenced by the protocol of ISDN interfaces B+B+D.
A constant ready state is usually required of such communication systems. Special hardware and software modules serve to guarantee these requirements, these modules being referred to, overall, as dependability systems and their assistance being used in order to limit the effects of disturbances. Crucial jobs which the dependability systems are responsible for are therefore trouble recognition, trouble localization, trouble evaluation and trouble reports. In the known ISDN communication system, the dependability systems are overall structured such that a sub-module for the module dependability system is formed in each module. These sub-modules are specifically adapted to the hardware structure and to the job of the appertaining program control module, but are always respectively identical in basic design. Due to the central significance and the wide-ranging jobs of the actual through-connection module in comparison to the remaining server modules, the dependability systems sub-module of the through-connection module differs noticeably from the dependability systems sub-modules of the remaining program control modules. Since the general domain of the dependability systems of such a communication system also include jobs that go beyond the domain of the program control modules, a system dependability systems sub-module is hierarchically higher-ranking over the individual dependability system sub-module, this system dependability systems sub-module being preferably arranged in the through-connection module. As a necessary precondition for error texts being capable of being output at error output equipment, these error texts providing indications regarding type of error, location of error or, respectively, cause of error, the dependability systems sub-modules of the individual program control modules transmit error information to this system dependability systems sub-module.